Process for the production of pure arsenious oxide from arsenical products



A'ug. 8, 1933. f

w scHoPPER l -,92L706 PROCESS FOR I THE PRODUCTION 0F PURE ARSENIOUSOXIDE FROM ARSENIGALPRODUCTS Filed Nov. 12, 1930 2 Sheets-#Sheet l .Figi

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50C 30C 770C mdw 8,' 1933 Y w. sczhHQPF'ER l 1,921,705

PROCIS FOR THE PRODUCTION OF PURE ARSENIOUS OXIDE FROM ARSENICALPRODUCTS Filed Nov. l2, 1930 2 Sheets-Sheet` 2 Rig. 3,

o9 Hz sa, 100'@ soga H, S04,n roo'C 700gr H2 $04 700"C 250 gf H2 so* 10ac 400g;- Hz S04 708 C' Patented Aug.

UNITED; sfr/iras PROCESS Fon 'rnc PATENT OFFICE 'PRODUCTION oF PURE QARSENIOUS OXIDE VFRIVI ARSENVICAL` PRODUCTS v Walter'Schopper, Hamburg,VGermany Application November' i2, i930, serial No. 495,266,

and in Germany November 26, 1929 1o claims. (onze- 144) This inventionrelatesrito. a process` for production oi pure' arsenious oxide fromarsenif cal products, su'ch as crude arsenical Yiue dust, containingarsenic in the form of arsenicus oxide. v

The *processes hitherto known for reiining crude arsenical ue arseniousoxide at high temperatures. processes, expelled, in `roastingror muiiiefurnaces,

ing to these Ydust utilize the volatility oi Accord* the` arseniousoxide is by the application of extraneous heat, and is then condensed,by coolingnally deposited in the furnace gases, being fidust chambers oralso by electrical gaspurication. These processes are attended with thequantities of highly arsenical health of vthe operators.

gerous to the drawback of producing large dust which is dan- More*over,fthe refining of the crude arsenious'oxide by volatilization isonly imperfectly effected when Y- the crude oxide contains antimo'ny, aportion of which, in such refined Furthermore, when case, passes` overwith the arsenious oxide and reduces its value.

antimony is present', a considerable portion of ther arseniousv oxide`must be left behind in the residue,

antimony also passes over, and prodlbulk ofthef ucts, which are alsoAccording to the since otherwise "the unsaleablafare obtained.

process of the present in vention,`these difculties are overcomefin thatthe production of the arsenious oxide,` inthe pure state, from products(such' as crude arsen-v ical ue dust) containing'same, is eiected byrecrystallization from aqueousv ample from solutio 'instead ofvolatilization as heretofore.

has hitherto been of arsenious oxide in water.

Solubility Tables of solution orex-y n in `dilute sulphuric acid, Littleabout the solubility In theV well-known Landolt-Brnstein (5th Ediknowntion), the solubility values for As203are not given above sequently,applicant the temperature oi 39.8

C. Cone first made a more thorough investigation into the` solubility ofarsenious ox ide, the result of which research is plotted as curves inFigs. 1,

2 and 3.

solubility of arsenious oxide/at temperatures of 1730 and 50 C. at C.,and Fig. 3 of the solution. Th

, Fig. `the rate at the boiling point` e curves were determined bykeeping an excess of arsenious oxide' stirred in the solvent employed,and ascertainingthe in# dissolved arsenious oxide in The water` creasedamount of samples drawn from time to time.

lost by evaporation was .continuously replenished.

A comparison of that the arsenious even .by dissolving the three`diagrams reveals` oxide can be recrystallized, it at boiling heat andrecooling the'hot-saturated aqueous or sulphuric acid solution. It was,

that the solubility largely increased by however, also ascertained oarsenious oxide is very treating it with the solvents A5263 and over.

2 the rate oi solution at temperatures above the boiling. point ofwater, f

tn is, by heating under pressure.; lFor exainp of53atznospheres-arsenious oxide'ican be dissolved in kwater to an extentcorresponding to a concentration of 200 grmsof A'szOaperl litre. Therate of solution oi' arsenious oxide'in water at 150 C, is shown in Fig.4;.- a

Based on this discovery, `the process. of Y,the present inventionconsists in extracting the ar-k senious oxide from crude arsenicalpowder, or other substances or mixtures containing "ar-` senious' oxide,by rneans of aqueousliquids, at ordinary orelevated'temperature-preferably at 'temperatures above 109 C., and forexample,"ati about 150' C.--and Ytheneiecting its deposition',1

in crystalline form, by cooling, after concentration if necessary.

According to the kind of originating material treated, the solvent mayconsist ci water, or or dilute acid (preferably sulphuric acid), oralso, insome cases, of, a weak solution, of alkali, containing for`example k2 grins. of i'ree 'caustic soda per litre.

at i500' C.-corresponding to va `pressure Eor example, the originating-arsenicalmaterial is heated with water, 1n an autoclave, at atemperature of 150 C., for severalhours under pressure and withstirring, highly concentrated solution of arsenious oxide is obtained.This solution is separated from the undissolved residue, for example ina filter press. On cooling, the arsenicus roxide separatesout, ink

by which means a a highly. pure state, with a content of 99.5% of ,Ithas also beenv ascertained that arsenious oxide displays an unusualtendencyto form supersaturated solutions.` Thus, for example',` asolution containing guns. of arseniouspoxide per litre, remainslimpidfor 24 hours, in spite of vthorough cooling, without manifestingany tendency todeposit AszOa crystals. Arsolution cooled down `tovnormal` temperature without crystallizing, andV not until several hourshave elapsed does the"` A5203 begin 'to vcrystallize4 out' gradually,the operation being, moreover, incomplete even after a periodof 4days or,Weeks Ex?y periments havel now revealed thatvthe difficulties icocontaining grms.V of` AszOa perlitre canffbe the content ofireesulphuric acid Yment of arsenical flue dust containing antimony. Inpresence of arsenious oxide, the solubility of antimonious oxide inwater at 150 C. amounts only up to 0.45 grin. of SbzO per litre, Whilstthe cooled solution is still able to retain 0.25V

grm. per litre in the dissolved state. Consequently, the presence ofvantimonious oxide does not aiect the rening ofV arsenious oxide by theprocess of the present invention.

The originating materials, such as arsenical ilue dust, sometimescontain soluble organic substances which,V in part, become associatedwith the arsenious oxide which crystallizes out, and stain it yellow. Insuch cases, in order to obtain a pure White product, it is advisable tostir up the hot-saturated As203 solution,Y prior to crystallization,with supercially active substances, such as finely ground active carbon,filter,` and not allow the As203 to crystallize out until this has'beendone.

1. Process for the recovery of arsenious oxide from substancescontaining the same, comprising extracting the arsenious oxide from theoriginating material by treating thelatter with an aqueous liquidcontaining no more alkaline reacting substance than isrepresented by 2grams of free alkali hydroxideper liter at a temperature above thenormal boiling point of the liquid and at a superatmospheric pressurecorresponding to said temperature, and depositing the arsenious oxidefrom the resulting solution by crystallization.

2. Process for the recovery of arsenious oxide from substancescontaining the same, comprising extracting the arsenious oxide from theoriginating material'by treating the latter with Water at a temperatureabove the normal boiling point of the liquid and at a superatmosphericpressure corresponding to said temperature, and depositing the arseniousoxide from the resulting solution bycrystallization. y

. 3. Process for the recovery of arsenious oxide from substancescontaining the same, comprising extracting the arsenious oxide from, the

originating material by treating the latter with' acidulated Water at atemperature above the normal boiling point of the liquid and at asuperatmcspheric pressure corresponding to said temperature, anddepositing the arsenious oxide from the resulting solution bycrystallization.

4. Process for the recovery of arsenious oxide from substances.containing the same, comprising extracting the arsenious oxide from theoriginating material by treating the latter with a mixture of water andsulphuric acid at a temperature above the normal boiling point of theliquid mixture andat a superatmospheric pressure corresponding to saidtemperature, and depositing the arsenious oxide romthe resultingsolution by crystallization.

5. Process for the recovery or" arsenious oxide from substancescontaining the same, comprising extracting the arsenious oxide from theoriginating material by treating the latter with an aqueous liquidcontaining no more alkaline reacting substance than lis, represented byk2 grams of free alkali hydroxide per liter at a temperature above thenormal boiling point of the liquid and at a superatmospheric pressurecorresponding to said temperature, and depositing the arsenious oxidefrom the resulting solution by cooling the same.

`temperature above the normal 6. Process for the recovery of arseniousoxide from substances containing the same, comprising extracting thearsenious oxide from the originating material by treating the latterWith an aqueous liquid containing no more alkaline reacting substancethan is represented by 2 grams of free alkali hydroxide per liter at atemperature above the normal boiling point of the liquid and at asuperatmospheric pressure `corresponding to said temperature, anddepositing the arsenious oxide from the resulting solution bycrystallization, subsequent to the addition of solid arsenious oxide incomparatively large amount to said solution.

'7. Process for the recoveryof` arseniousoxide from substancescontaining the saine, comprising extracting the arsenious oxide from theoriginating material by treating the' latter With. an aqueous liquidcontaining no more alkaline reacting substance than is represented by 2grams of free alkali hydroxide per liter at a temperature above thenormal boiling point of the liquid and at a superatmosplieric pressurecorresponding to saidtemperature, and ldepositing the arsenious oxidefrom the resulting solution by crystallization, subsequent totheaddition, with stirring, of solid arsenious oxide in comparativelylarge amount to said solution. y

8. Process for the recovery of arseniousV oxide from substancescontaining the same, comprising extracting the arsenious oxide from theoriginating materialby treating the latter with an aqueous liquidcontaining no more alkaline reacting substance than is represented by 2grams of free alkali hydroxide per liter at a boiling point of theliquid and at a superatmospheric pressure corresponding to saidtemperature, and depositing the arsenious oxide from the resultingsolution by crystallization', after decolorationof said solution with adecolorizing medium.V

9. Process for the recovery of arsenious oxide from crude arsenical'flue nious oxide and antimony, comprising extracting the arsenious oxidefrom the flue dust by treat-` ing the latter with an aqueous liquidcontaining no more lalkaline reacting substance than is represented by 2Ygrains of free alkali hydroxide per liter at a temperature above thenormal boiling point of the liquid and at a superatmospheric pressurecorresponding to said temperature, and separating the Yarsenious oxidefrom the resulting solution by crystallization in a directly marketableform by virtue of its purity, its intense white colorand its high specicgravity.

l0. Process for the recovery of arsenious oxide from metallurgicalintermediateand waste productsl containing arsenious oxide and antimonyand considerable quantities of mineral and other constituents,comprising extractingy the arsenious oxide from the originating thellatter With an aqueous liquid at a temperature above the normal boilingpoint of the liquid and at a'superatmospheric pressure corresponding tosaid temperature, and separating the arseniousroxide from the resultingsolution by crystallization in a directly marketable form by virtue ofits purity, its intense White color and its high specific gravity.

WALTER sCHoPPEa.

material by treatingY dust containing arse-

